Abstract: Based on the analysis of spectral characteristics of colour-treated blue diamonds from the routine tests, the identification of this kind of diamonds is confirmed. The infrared spectra reveal that the diamonds are type Ⅰa, and show H1a center related to radiation and annealing, which is reflected by a characteristic peak at 1 450 cm^-1. UV-Vis-NIR spectra shows obvious GR1 center and weak centers including ND1 center, 3H center and N3 center. According to the comprehensive analysis, the two samples are diamonds of natural origin. They have been subjected to irradiation followed by low-temperature annealing. The blue colour is mainly induced by GR1 center.